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Review 09/2010 page
RF System for Electron Collider RingRF System for Electron Collider Ring
Haipeng Wangfor the team of R. Rimmer and F. Marhauser, SRF Institute
and
Y. Zhang, G. Krafft and S. Derbenev, CASA
Review 09/2010 page
Medium Energy EIC Top Layout
Three compact rings:• 3 to 11 GeV electron• Up to 12 GeV/c proton (warm)• Up to 60 GeV/c proton (cold)
Review 09/2010 page
Electron collider ring figure 8 layout
3
MEIC collider ring134.989 m
R=57.495 m
60°
379.609 m
20.000 m
239.167 m
dipole magnet bending radius m 57.495 57.495average beam current A 3 0.13electron beam energy GeV 5 11synchrotron radiation power per ring MW 3.85 3.91energy loss per turn MeV 1.28 30.07radiation power per unit arc length kW/m 5.331 5.411figure 8 circumference m 1000 1000electron revolution frequency kHz 299.79 299.79RF harmonic number 2496 2496RF cavity's frequency MHz 748.50 748.50revolution time ms 3.3356 3.3356bunch spacing m 0.401 0.401
RF insertion
Low energyHigh current
High energyLow current
Straights cross angle deg 60.000Circumference m 1000.000
Arc radius m 57.495Figure 8 width m 134.989Figure 8 length m 379.609Straight length m 239.167
Insertion straight length m 20.000Dipole compacting factor % 60
Review 09/2010 page
Electron Beam Stacking Structure for 5GeV
4
<3.3 ps(<1 mm)0.4 pC
1.334 ns (40 cm)
0.750 GHz
10-turn injection 33.3 μs (4 pC)
40 ms (~5 times radiation
damping)25 Hz
40 s (1000 bunch trains), average current=3 A
Microscopic bunch duty factor 2.47x10-3 average current=0.3 mA
Macroscopic bunch duty factor 8.33x10-4
From CEBAF SRF Linac
Stored beam in collider ring
revolution time=3.33 μs, 2501 bunches per ring
Review 09/2010 page
Existing RF systems in storage rings: normal conducting
5
BESSY
PEP-II
Two examples
Rimmer and Allen etc
Marhauser and Weihreter etc
Review 09/2010 page
Existing RF systems in storage rings: superconducting
6
Two examples
CESR-III B-cell
KEKB-TRISTANFuruya and Akai etc.
Padamsee and Chojnacki etc
Design Parameters Units Original CESR-III, Cornell Univ. Original KEKB, Japan
cavity parameters CESR-III Cavity KEKB-HER cavity
frequency MHz 499.765 509number of cell 1 1
R/Q = Ueff^2/(w*W) Ohm 89.0 93.0R/Q/cell Ohm 89.0 93.0
material independent geometry factor G = Rs*Q0 Ohm 270.0 250.0R/Q*G Ohm 24030 23250
acitve length m 0.3 0.243insertion length m 2.86 3.01
operating temperature Kelvin 4.2 4.2
BCS surface resistance RBCS nΩ 97.2 100.8
residual surface resistance assumed Rres nΩ 13.0 13.0
total surface resistance Rs nΩ 110.2 113.8Q0 5.0E+08 2.2E+09
shunt impedance (R=Ueff^2/P) MΩ 4.5E+04 2.0E+05input power (total losses) kW 324.9 571.2Pcavity (surface losses) kW 0.00761 0.00079Pbeam (beam loading) kW 320.00 562.50
Pbeam (beam loading on crest) kW 324.9 571.2average beam current A 0.55 1.4
minimum gap voltage required kV 581.8 401.8accelerating gradient MV/m 1.97 1.68
Qext matched Q0/(1+Pbeam/Pcavity) 2.00E+05 8.90E+04coupling factor (Q0/Qext) 2.50E+03 2.47E+04
total radiated power MW 1.28 4.50energy loss per turn MeV 2.33 3.21
beam energy GeV 5.3 8rf effective accelerating voltage MV 2.33 3.21
synchronous phase, 0 is on crest deg 10 10rf peak voltage required MV 2.363 3.264
number of cavities needed 4 8insertion length m 11.440 24.080
straigh section length in storage ring m
Preliminary Cost Exercise from BNL per Jim Rose 2008costs per cavity $ $1,200,000
total investment costs + RF power $ $3,395,000total investment costs (cavities only) $ $4,800,000
total costs (w/o power bill) $13,580,000cryoplant $
RF to AC power per year $
operational costs per year $ could favor SRF after 5-10 years could favor SRF after 5-10 years
Review 09/2010 page
Synchrotron radiation power
RF system in storage ring: Technology of choice
7
High CurrentLow Energy
High EnergyLow Current
Klystron power
Power coupler and RF window
Beam excited HOMs
HOM damping by waveguide or coaxial coupler
Liquid heliumCooling, 4.2K
DI water cooling<300K
High gradient for CW
Bunch head-tail instability
Large beam aperture
ceramics
ferrites
Low RF Frequency
Low gradientfor CW
Normal conducting cavity
RF acceleration
Low broadband and narrow band HOM impedance cavity
)()(
)()/(108575.8
4435 mAI
m
GeVEGeVmPrad
Superconducting cavity
Warm HOM windows and loads
<600kW for CW RF power
Beam loading control
Review 09/2010 page
Design Parameters Units MEIC3 MEIC4cavity parameters BESSY type cavity scaled BESSY type cavity scaled
frequency MHz 748.5 748.5number of cell 1 1
R/Q = Ueff^2/(w*W) Ohm 230.8 230.8R/Q/cell Ohm 230.8 230.8
material independent geometry factor G = Rs*Q0 Ohm 234.0 234.0
R/Q*G Ohm 54007 54007acitve length m 0.2 0.155
insertion length m 0.333 0.333operating temperature Kelvin >300 >300
BCS surface resistance RBCS nΩ n/a n/a
residual surface resistance assumed Rres nΩ n/a n/a
total surface resistance Rs nΩ n/a n/a
Q0 30000 30000shunt impedance (R=Ueff^2/P) MΩ 6.92 6.92
input power (total losses) kW 551 549Pcavity (surface losses) kW 333.196 3.913Pbeam (beam loading) kW 197.457 493.775
Pbeam (beam loading on crest) kW 217.869 544.821average beam current A 0.13 3
minimum gap voltage required kV 1518.9 164.6accelerating gradient MV/m 10.84 1.17
Qext matched Q0/(1+Pbeam/Pcavity) 1.81E+04 2.14E+02coupling factor (Q0/Qext) 1.65E+00 1.40E+02
total radiated power MW 6.52 6.42energy loss per turn MeV 50.12 2.14
beam energy GeV 11 5rf effective accelerating voltage MV 50.124 2.140
synchronous phase, 0 is on crest deg 25 25rf peak voltage required MV 55.305 2.361
number of cavities needed 33 13insertion length m 11.0 4.3
straigh section length in storage ring m 20.000 20.000Preliminary Cost Exercise
costs per cavity $total investment costs + RF power $
total investment costs (cavities only) $total costs (w/o power bill)
cryoplant $RF to AC power per year $operational costs per year $
Scaled RF system for MEIC Electron ring: normal conducting
8
BESSY:<100kWEacc=6MV/mConditioned up to 30kW CW in 5 days.
11GeV 5GeV
Marhauser and Weihreter
Review 09/2010 page
Design Parameters Units MEIC1 MEIC2cavity parameters CESR Cavity Scaled, high energy CESR Cavity Scaled, low energy
frequency MHz 748.5 748.5number of cell 1 1
R/Q = Ueff^2/(w*W) Ohm 89 89R/Q/cell Ohm 89.0 89.0
material independent geometry factor G = Rs*Q0 Ohm 270.0 270.0
R/Q*G Ohm 24030 24030acitve length m 0.2 0.2
insertion length m 1.91 1.91operating temperature Kelvin 4.2 4.2
BCS surface resistance RBCS nΩ 218.0 218.0
residual surface resistance assumed Rres nΩ 13.0 13.0
total surface resistance Rs nΩ 231.01 231.0
Q0 1.17E+09 1.17E+09shunt impedance (R=Ueff^2/P) MΩ 1.04E+05 1.04E+05
input power (total losses) kW 513.7 544.8Pcavity (surface losses) kW 0.12323 0.00026Pbeam (beam loading) kW 465.43 493.78
Pbeam (beam loading on crest) kW 513.5 544.8average beam current A 0.13 3
minimum gap voltage required kV 3580.3 164.6accelerating gradient MV/m 19.73 0.91
Qext matched Q0/(1+Pbeam/Pcavity) 2.80E+05 5.59E+02coupling factor (Q0/Qext) 4.17E+03 2.09E+06
total radiated power MW 6.52 6.42energy loss per turn MeV 50.12 2.14
beam energy GeV 11 5rf effective accelerating voltage MV 50.12 2.14
synchronous phase, 0 is on crest deg 25 25rf peak voltage required MV 55.305 2.361
number of cavities needed 14 13insertion length m 26.734 24.825
straigh section length in storage ring m 20.000 20.000Preliminary Cost Exercise from BNL per Jim Rose 2008
costs per cavity $ $1,200,000total investment costs + RF power $ $3,395,000
total investment costs (cavities only) $ $29,789,600total costs (w/o power bill) $84,279,742
cryoplant $RF to AC power per year $operational costs per year $ could favor SRF after 5-10 years
Scaled RF system for MEIC electron ring: superconducting
9
11GeV 5GeV
JLab High Current 750MHz, 5-cell, 1A cavity
Only single-cell is preferred due to a heavy HOM damping requirement in storage ring,But space is limited.
Rimmer and Wang etc
Review 09/2010 page
Initial HOM Analysis: beam current excitation
10
FFT
S. H. Kim and H.Wang
•Time averaged HOM power normalized to R/Q (W/= Amp2) is current square drive term. It has no information of the cavity but with assumed HOM damping Qext. • For example, if we have a HOM resonated at 2.25GHz with R/Q of 10 and Q external of 100 , we have 1kW HOM power from the beam in this mode.• When we design a high current cavity, we have to avoid HOM frequencies sitting on the beam excitation resonances.H. Wang etc PAC2005 TPPT086.
Review 09/2010 page
Initial HOM damping analysis: Impedance and HOM power
11
BESSY CWCT copper cavity impedance measurement sMarhauser and Weihreter, EPAC 2004
Impedance scaling from BESSY NC RF cavity in same shape but in different frequency scale:• monopole modes around 2.25 GHz have to be avoid by either changing the cavity shape (safe to park) or damping totally with Qext< 100, otherwise 50kW (on resonance HOM power will come out to the HOM loads.• Following is an example (H. Wang etc PAC 2005) for JLab High Current 5-cell cavity design to avoid HOM resonance by choosing different cavity shapes.
0
36
72
108
144
180
2.90 2.92 2.94 2.96 2.98 3.00 3.02 3.04 3.06 3.08 3.1010-1
100
101
102
103
104
105
106
light cone line
R/Q/cell=1.25(/cell)
JLab-LL Re-entrant JLab-LL-modified ILC-LL Rounded Pillbox Spherical Section
Frequency f (GHz)
Pha
se A
dvan
ce
(de
g)
P=120(W/)*1.25(/cell)*5(cell)=750W
1A, 750MHz CW laser, Qext
=10^4 1A, 750MHz CW laser, Q
ext=10^3
TM030 mode
Tim
e A
vera
ged
HO
M P
ower
/ (R
/Q)
(W/
)
Review 09/2010 page
MEIC electron ring RF system Summary: Pros and Cons
12
SCRF favors to High Energy, Low Current Operation NCRF favors to Low Energy, High Current Operation
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